Negative feedback amplifier



July 16, 1940. H. WERRMANN 'NEGATVE FEEDBACK AMPLIFIER Filed oct. 23,1937 AMPLIFIER INVENTOR HELL/VUT PREM 4N/v BY ATTORNEY Patented July-16,y1940 PATENT OFFICE NEGATIVE FEEDBACK AIWPLIFIER Y Hellmut Werrmann,Berlin-Charlottenburg, Germany, assignor to Siemens & Halske, Aktien`gesellschaft, Berlin-Siemenstadt, Germany Application October 23, 1937,'Serial No. 170,563 In Germany December 3, 1.936

1 claim. (o1. 179-171) It is known that linearity of amplier circuitscan be obtained by employing a negative feedback. To provide a possiblyfavorable linearity itl is desirable to render the degree of thenegative 5 feedback as high as possible. This degree is limited by theappearance of natural oscillations. It has been proposed to extend thislimit as far as possible by the use of additional stabilizing means. Thestabilizing means are inserted in the feedback circuit and serve forinfluencing the phase angle and the 'damping in the coupling path suchthat the amplifier remains stable in case of a high degree of feedback.The additional stabilizing means are of rather complicated structure, ifits stabilizing action is to be a considerable one.

In accordance with the present invention a more favorable exploitationof such known amplifier circuit is brought about in that the stabilizingmeans which shall not be dispensed with in the interest of the stabilityof the entire circuit, are so adapted vand dimensioned that theyinfluence at the same time the frequency pattern of the amplifier in thedesired manner. Additional means .which hitherto had to be provided forthe purpose of reducing distortion are no w omitted, and the entirestructure of the amplifier circuit will be simplified. It is especiallysuitable to compensate by an appropriate design ofv the stabilizingmeans the decrease of the degree of amplification caused at the limitsof the transmission range due to the transformers provided at the inputand output of the amplifier. These stabilizing means may, however, beutilized to compensate forthe distortions 35 caused by the transmissionelements such as lines connected to the amplifier. n vAn amplifier tubeV, of any construction, is shown in the drawing connected to the inputcircuits and output circuits across the transformers T1 and T2. Thefeedback path, containing as a stabilizing member a single (or several)bridged T-circuit, is coupled in the known manner with l the gridcircuit and plate circuit of the amplifier across two bridge circuits B1and B2. The bridged T-circuit consists of ohmic series resistors Z1 andZ2 and parallel resistors R and R1; the inductances L, L1, and thecondensers C, C1. If care is taken by a proper design of the bridgingelement and of the parallel element, that for instance for the 5 lowerfrequencies the damping increases slowly within a suitable range, thedegree of amplification will likewise increase for these frequencies,and the decrease caused by the transformers will therebybe compensated.A correspondingpatl0 tern of the amplification curve can be attained atthe lupper frequency limit of the transmission range by meansof acorresponding stabilizing member necessary for stabilizing the amplifierat the high frequencies. In like manner, also, the 15 distortionproduced by the connected transmission lines can be eliminated. However,the invention is especially suited for compensating .the distortionsAcaused by the transformers, since this compensation can be accomplishedwithout adj 20 ditional circuit means.

What is claimedis: In an amplifier system adapted to transmit a widerang-e of frequencies of the type comprising Van amplifier having'aninput transformer and 25 an youtput transformer, a bridge networkconnected across the secondary of the input transformer, a bridgenetwork connected across the primary of the output transformer, adegenerative feedback path connected between the two bridge 30 networks,said feedback path includinga netv work whose constants are chosen tocompensate for the decrease of the degree of amplification caused at thelimits of said range by said input and output transformers, and said"compensation network consisting of a pair of r-esistorsin series in saidfeedback patha series path of a condenser, resistor vand inductanceconnected between the junction of said resistors and ground, and a shuntpath across said pair of series resistors comprising a condenserinductance and resistor in parallel toeach other.

W'ERRMANN.

